Genetic Divergence of <i>Toxoplasma gondii</i> Strains Associated with Ocular Toxoplasmosis, Brazil

Khan, Asis; Jordan, Catherine; Muccioli, Cristina; Vallochi, Adriana Lima; Rizzo, Luiz Vicente; Belfort, Rubens; Vítor, Ricardo Wagner Almeida; Silveira, Cássio; Sibley, L. David

doi:10.3201/eid1206.060025

Cited by 277 publications

(195 citation statements)

References 39 publications

Supporting

Mentioning

164

Contrasting

Unclassified

Order By: Relevance

“…In acquired ocular toxoplasmosis, an unusual abundance of type I or recombinant genotypes I/III have been found in USA (Grigg et al, 2001c). The high occurrence of ocular toxoplasmosis in Brazil has been attributed to atypical or recombinant genotypes circulating in this country (Khan et al, 2006). This may also explain the high frequency (20 % of 97 cases) of ocular involvement in the Victoria outbreak, in British Columbia where an atypical cougar isolate was suspected (Burnett et al, 1998), and the 100-fold higher incidence of ocular toxoplasmosis in patients born in Africa compared to patients born in Britain (Gilbert et al, 1999).…”

Section: Genotypes and Expression Of Toxoplasma Virulence In Humansmentioning

confidence: 99%

Toxoplasma gondii, “new” genotypes and virulence

Dardé¹

2008

Parasite

149

113

View full text Add to dashboard Cite

Summary :Toxoplasma gondii has been described as a parasite with a low genetic diversity and a clonal population structure. The three main clonal lineages designated as type I, II or III largely predominate in Europe and North America. But strains not related to these main lineages circulate, notably, in other continents. They possess a shuffled combination of alleles that typify the three clonal types and unique polymorphisms detected by multilocus analysis. The population structure of Toxoplasma in these continents is also characterized by a higher genetic diversity associated with a lower linkage desequilibrium suggesting a role for genetic exchange. Due to their genomic diversity, it is difficult to draw global conclusions about their virulence. However, most of them are virulent in mice at isolation. Several reports also suggest a higher pathogenicity in humans and an association with ocular toxoplasmosis or severe cases of acquired toxoplasmosis in immunocompetent patients. T he three main types respond to the criteria for a clonal population structure of Toxoplasma (isolation of identical multilocus genotypes over large geographic areas and at interval of several years, and a strong linkage disequilibrium) (Tibayrenc et al., 1991). This simple clonal structure is accompanied by a low genetic divergence between the three main lineages (only ≈ 2 % divergence at the DNA sequence level between lineages). A large majority (84 %) of the of the single nucleotide polymorphisms (SNPs) identified among the three types are type I and II SNPs, type III polymorphisms (only 16 %) being located mainly on chromosome IV (Boyle et al., 2006). The assymetrical distribution of SNPs on chromosomes indicates that types I and III are second and first generation offspring, respectively, of a cross between a type II strain and one of two ancestral strains. The limited genetic diversity within each of these lineages and the low divergence between lineages strongly suggest that these three clonal lineages have expanded as the dominant strains relatively recently, from a common ancestor 10,000 years ago (Su et al., 2003).

show abstract

Section: Genotypes and Expression Of Toxoplasma Virulence In Humansmentioning

confidence: 99%

Toxoplasma gondii, “new” genotypes and virulence

Dardé¹

2008

Parasite

149

113

View full text Add to dashboard Cite

show abstract

“…6 The geographic differences in the epidemiology of OT reflect the genetic variability in the parasite strains occurring in the respective regions; that is, strains from South America, responsible for the often severe clinical course of toxoplasmosis on this continent, are often type-1, or recombinant, and generally divergent from those in Europe and North America where a vast majority of all isolates belongs to type-2. [8][9][10][11] In Serbia, the seroprevalence of toxoplasmosis is currently estimated at 30-35% 12 and type-2 genospecies has been isolated. 13 As fetal infection may only develop following maternal primary infection in pregnancy, congenital toxoplasmosis is a preventable disease; therefore, the incidence of OT of congenital origin may be expected to decrease in line with successful prevention strategies implemented in a particular milieu.…”

Section: Introductionmentioning

confidence: 99%

Clinical pattern of ocular toxoplasmosis treated in a referral centre in Serbia

Kovačević-Pavićević

Radosavljević

Ilić

et al. 2012

Eye

View full text Add to dashboard Cite

show abstract

“…Nonetheless, cases of congenital toxoplasmosis in the chronic phase have been reported in immunocompetent females, indicating the possibility of reinfection in humans (Dollfus et al 1998, Silveira et al 2003, Kodjikian et al 2004, Elbez-Rubinstein et al 2009). In mouse models, reinfection occurs when parasites are of different clonal genotypes (Araújo et al 1997, Dao et al 2001, but no information is available on host co-infection with recombinant T. gondii strains, which are commonly found in Brazil , Khan et al 2006, Dubey et al 2007.…”

mentioning

confidence: 99%